When was the last time you repaired/verified your drives with Disk Utility?
How much free disk space do you have on the boot volume? You should leave about 20GB to 25GB free for the OS.
Do a smc reset.
Boot in safe mode then reboot normally.
Open Activity Monitor to see if there is some process hogging the cpu or there are memory problems. With respect to understanding the memory behavior shown in your Activity Monitor read the following: